By comparison with domestic environmental issues, international environmental diplomacy is distinguished by the far greater role of the Executive Branch, and in particular the President, in making law. This essay explores the legal consequences of the President's dual role in international environmental diplomacy: his duty faithfully to execute statutory mandates adopted by Congress while also serving as the Nation's chief diplomat and negotiator of international agreements with foreign powers. The piece discusses the legal and policy dynamics surrounding two concrete examples affecting domestic and international environmental policy, in which Presidential power assumes dramatically different forms: (1) climate change, and in particular the negotiation and implementation of the Kyoto Protocol; and (2) international trade agreements, such as the Uruguay Round and NAFTA.